PROJECT SUMMARY An antibiotic susceptibility test (AST) determines whether or not bacterial isolates from a patient?s blood, wound specimens, or urine are susceptible to administered antibiotics. Standard antibiotic susceptibility tests measure the growth of sampled bacteria in administered antibiotics and require long cell culturing steps. This R03 application proposes a fundamentally different method, in which the activity of surface-adhered bacteria will be monitored. Bacteria that are adhered on a surface are known to exhibit incessant nanomechanical fluctuations (random vibrations). This study aims to prove that these fluctuations are due to metabolic activity of bacteria and are correlated with the antibiotic response. As a first step, fluctuations of clinically- relevant bacteria, which possess different cellular morphologies and different mechanisms of motility, will be measured. Then, the antibiotic susceptibility of these bacteria will be correlated with their nanomechanical fluctuations. The proposed approach to antibiotic susceptibility testing is phenotypic and label-free. It will eliminate the need for extensive culturing and allow for rapid testing. Finally, it is simple enough that it might have the potential to be used at point- of-care settings.